Liquid crystal display devices and touch panels have become widely used in large-size electronic equipment, such as personal computers and TV sets, small-size electronic equipment, such as car navigation devices, mobile phones and electronic dictionaries, and display equipment, such as office and factory automation equipment. In these liquid crystal display devices and touch panels and in such devices as solar cells and lighting devices as well, a transparent conductive film is used in wiring lines, pixel electrodes or some terminals required to be transparent.
Conventionally, an ITO (Indium-Tin-Oxide), an indium oxide, a tin oxide, or the like has been used as the material of a transparent conductive film since the oxide exhibits high transmissivity with respect to visible light. Thus, patterned transparent conductive films made from the above-described materials prevail among electrodes provided in a substrate or the like for liquid crystal display devices.
As a method for patterning a transparent conductive film, there is generally used a method in which, after a transparent conductive film is formed on a base material, a resist pattern is formed by a photolithographic method and predetermined portions of the conductive film are removed by wet etching, thereby forming a conductive pattern. In the case of an ITO film and an indium oxide film, a mixed liquid composed of two liquids, i.e., hydrochloric acid and ferric chloride, is often used as an etching liquid.
An ITO film and a tin oxide film are generally formed by a sputtering method. In this method, the nature of the transparent conductive film is changeable, depending on a difference in sputtering system, sputtering power, gas pressure, substrate temperature, the type of ambient gas, and the like. A difference in the quality of the transparent conductive film due to a variation in sputtering conditions can be a cause for the variation of an etching rate at the time of wet-etching the transparent conductive film. Thus, the difference is liable to cause degradation in product yields due to patterning failure. In addition, the above-described method for forming conductive patterns takes a long process time and is burdensome costwise since the method goes through a sputtering step, a resist formation step and an etching step.
In recent years, attempts have been made to form conductive patterns using materials alternative to an ITO, an indium oxide, a tin oxide and the like, in order to cut down the above-described problems. For example, Patent Literature 1 cited below discloses a conductive pattern formation method in which after a conductive layer containing conductive fiber, such as silver fiber, is formed on a substrate, a photosensitive resin layer is formed on the conductive layer, and then the photosensitive resin layer is exposed and developed from thereabove through a pattern mask. Patent Literature 2 cited below discloses a conductive pattern formation method using a photosensitive conductive film.